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C#, C++, and Java: Types, Templates, & Parameterized Factories 

Too Much Knowledge?


For the tenured C++ developer, both C# and Java have their thrills - as well as their chills.

For many, one of the chills can occur when your templates are prematurely inspected by that Java or C# Compiler. While absolutely similar to C++ in many ways, in other ways the C# and Java compilers arguably check templates far too early to ensure that a class member might (or might not) be there!

Templates (aka "parameterized types")


Take for example the need to return a generic object - classically referenced as a generic type T - via a template. While templates are common to C++, Java, and C# (order of plagiarism), there are some very subtle differences in when those me-too compilers allow templates to be applied.

In C++, for example, template implementations are comparatively overlooked until they are required. Ignoring templates until they are used means that while the intention behind:


class MyClass<T> {
...
}


-is clear in all 3 languages, the compile-time realties can be very different, indeed.





How different? Well, the intent to declare a T as our yet-to-be defined class is obvious. But what if we want T to also be used in a certain way? What if we need to be sure that T has a T.read(RandomAccessFile), for example?

Interface Compliance


Upon first blush, one might quite naturally assume that a C# or Java interface can be used. Something like (in Java):


class MyClass<T implements MyCommonStufToDo> {
...
}


Yet, try as we might, at the time of this writing there seems to be no way in either C# or Java to do what - because of a far more relaxed template-checking policy - we can easily do in C++. Namely, insure that our T has implemented a few member functions.

After a few head-scratching moments however, there IS indeed another way to proffer BOTH a reusable template implementation, as well as to assure required operational support, too: Just provide your template with an Object-Factory as a template Interface.

Templates & the Factory Interface



While the C++ way of assuming class-members for a parametrized type is impossible in C# and Java, one great work-around is to leverage a touted feature: The Java & C# need to avoid multiple-inheritance, by using Interfaces. Rather than having MyCommonStufToDo a descendant of T therefore, we simply provide a factory for T where needed:


class MyClass<T> {
public MyClass(MyCommonStufToDo factory) {
this.factory = factory;
}
}


Okay - so let's call providing an interface to use as factory PART ONE. --What did THAT do for us?

Trudging Onward...



Depending upon what we want to do, a parameterized "T factory" can be very handy, indeed! For the purposes of this article, let's assume that we want to read a T from a RandomAccessFile.

In Java, our interface might look like:


public interface iIndexReader<T> {
public T read(RandomAccessFile raf);


Now comes the beautiful part - where using that factory-parameter makes the most sense!

Let's update MyClass to re-use that read member function. To wit:


public T read(long iQuest) {
if (open()) {
long iTally = FileIndex.RecordCount(index);
if (iQuest < iTally) {
IndexLogical logical = new IndexLogical(iQuest);
IndexPayload pay = FileIndex.Read(index, logical);
if (pay.isNull()) {
return null;
}
try {
reader.seek(pay.id);
} catch (IOException ex) {
close();
return null;
}
T result = factory.read(reader);
close();
return result;
}
}
return null;
}


That T result = factory.read(reader); is the important bit. -If you are not familiar with the rest, then feel free to ignore the use of my com.soft9000.dbo file-indexing framework (IndexLogical, etc..)

That factory.read(reader) demonstration nicely completes a succinct pattern for C# and Java. I have found it to be a viable stratagem. One that allows us to have our re-use (templates), strong-type checking (T), as well as a ubiquitous signature guarantee (interface<T>) for a yet-undefined template-type, as well.

Enjoy!

-Rn


p.s. If I have given the reader the impression that C++ template support is superior to those of Java or C#, make no mistake: When it comes time to link-together objects - certainly those that have been compiled between divergent Standard C++ Template libraries - then the tao of the template is an entirely different story! If we do not have the source code, then give us C# or Java over template-laden C++, A-N-Y-T-I-M-E! :)

(Come to think of it, knowing several technologies is far, far, better than knowing just a few. -Knowing the alternatives allows one to avoid the nearsighted language-camps & technology "religious wars." --We are instead free to pick the right tool, for the right job, for the right-reasons! (requirements, anyone?))



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Simple XML Serialization 

Peeves


Having formerly been a Principle Software Development Engineer at Informix - the maker of the fastest database of the era - I can say that many senior folks simply *HATE* the way people use databases today. -Not only do folks use them to store everything from web-site logging to SOX telemetry, but few developers know how to scale them properly... let alone document their schema.

Bottlenecks


Indeed, when doing performance reviews, I often find that the first performance logerjam is most often found at the persistence layer. Not only is the way people save data at fault, but the sheer range of data being stored in a single database - at the same time - is often a critical performance problem.

Bottom Lines


In general folks simply need to remember that databases are merely managing files! -Indexed or not, there is purely no magic in the word d-a-t-a-b-a-s-e. The implementation of each and all eventually boils down to caching, latencies... and bits-on-a-disk.

By way of liberating the databases from gratuitous data storage, I have found many interface-free (emphasis on having a FREE interface, not on having NO interface) -ways of storing varying amounts data. From using spreadsheet-savvy formats - like CSV, TDF, and SDF - to using editors & XML-Tagged data - options abound. Certainly when managing any day's worth of data in an appropriately-named location!

Of course, with a little help, simple data formats are great even when storing huge amounts of data. (our DBO package is an example.) But certainly when the envisioned amount of data can be stored in-memory... or for personal edit-and-use, why use a database at-all?

ClassIO


When we resolve the need to store data down to the brass tax of it all, we can see that the first challenge we solve is one of demarcation. Be the data binary or text, how to delimit them?

Once we resolve upon a human-editable form, for many it next all comes down to simple, traditional ASCII. Yes, yes - we can do a lot more - but 80% of an intelligent developer's raw data-collection activities, localized text is enough for most of the planet.

Interestingly, when is comes to XML readers & writers, many have found - for just about the same percentage - that well-formed XML is good enough, too!

So allow me to share ClassIO. -While far, far from the be-all and end-all to XML generation (the present version has yet to implement XML Attributes, for example) for most of what most-of-us might like to do, it will get the job done.

You can download the present version at Sourceforge.NET.

How ClassIO Works


ClassIO supports a simple command-line interface. -It also generates Java.

To start ClassIO up, enter:

java -jar com.soft9000.ClassGenerator.jar

By way of shoring off what ClassIO can do, enter:

java -jar com.soft9000.ClassGenerator.jar pkg cUsr Name Email


Here is the generated code. Note the isNull(a personal favorite), the copy constructor, an equality operation, object-assignment, as well as the ability to read an entire set of objects from a file:


package pkg;

import java.io.File;
import java.util.ArrayList;
import javax.xml.parsers.*;
import javax.xml.xpath.*;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;


public class cUsr {
public cUsr() {
}
public cUsr(cUsr ref) {
if(ref == null) ref = new cUsr();
this.Name = ref.Name;
this.Email = ref.Email;
}
private String Name = "";
private String Email = "";

public String getName() {
return Name;
}
public String getEmail() {
return Email;
}
public void setName(String ref) {
if(ref == null) ref = "";
this.Name = ref;
}
public void setEmail(String ref) {
if(ref == null) ref = "";
this.Email = ref;
}
public boolean isNull() {
if(this.Name == null) return true;
if(this.Name.equals("") == false) return false;
if(this.Email == null) return true;
if(this.Email.equals("") == false) return false;
return true;
}
public boolean equals(cUsr ref) {
if(this == ref) return true;
if(ref == null) ref = new cUsr();
if(this.Name.equals(ref.Name) == false) return false;
if(this.Email.equals(ref.Email) == false) return false;
return true;
}
public void assign(cUsr ref) {
if(ref == null) ref = new cUsr();
this.Name = ref.Name;
this.Email = ref.Email;
}
private boolean set(Node val) {
if(val == null) return false;
NodeList nodes = val.getChildNodes();
int nelem = nodes.getLength();
for (int ss = 0; ss < nelem; ss++) {
Node node = nodes.item(ss);
if (setField(node.getNodeName(), node.getTextContent()) == false) {
return false;
}
}
return true;
}
private boolean setField(String sTag, String sValue) {
if(sTag == null || sValue == null) return false;
if(sTag.equals("Name")) {
setName(sValue);
return true;
}
if(sTag.equals("Email")) {
setEmail(sValue);
return true;
}
return true; // XML has meta stuff - just accept it.
}
public static cUsr[] FromXML(File file) throws Exception {
ArrayList<cUsr> list = new ArrayList<cUsr>();
DocumentBuilderFactory domFactory =
DocumentBuilderFactory.newInstance();
domFactory.setNamespaceAware(false);
DocumentBuilder builder = domFactory.newDocumentBuilder();
org.w3c.dom.Document doc = builder.parse(file);
XPath xpath = XPathFactory.newInstance().newXPath();
// XPath Query for showing all nodes value
XPathExpression expr = xpath.compile("//cUsr");
Object result = expr.evaluate(doc, XPathConstants.NODESET);
NodeList nodes = (NodeList) result;
for (int i = 0; i < nodes.getLength(); i++) {
Node val = nodes.item(i);
cUsr ref = new cUsr();
if(ref.set(val) == false) throw new Exception("Error: Invalid xml data.");
list.add(ref);
}
cUsr[] dresult = new cUsr[list.size()];
list.toArray(dresult);
return dresult;
}
public String toXml() {
StringBuilder sb = new StringBuilder();
sb.append("<cUsr>\n");

sb.append("<Name>");
sb.append(Name);
sb.append("</Name>\n");

sb.append("<Email>");
sb.append(Email);
sb.append("</Email>\n");

sb.append("</cUsr>\n");
return sb.toString();
}
public static String ToXml(cUsr[] array) {
StringBuilder sb = new StringBuilder();
sb.append("<pkg>\n");
for(int ss = 0; ss < array.length; ss++) {
sb.append(array[ss].toXml());
}
sb.append("</pkg>\n");
return sb.toString();
}
};


While adhering to the JavaBean Specification (i.e. the above could quickly become 'import java.io.Serializable'), the use of XML solves the perpetual data-conversion efforts required when even lightly changing a Serializable class definition. 'Gotta love the POJO.

Easier Maintenance


Since we have come to the above observations, note that if you plan to re-generate your ClassIO code - or even if you don't ;-) -then you should consider using inheritance. While few developers consider the possibility these days, using a tool like ClassIO to update a base parent-class is to be preferred to endlessly merging code.

-Enjoy!

-Rn



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Of UML, VISIO, & Developers? 
When is a scenario, not a scenario?

When we are using UML under VISIO, of course!

If you ever have received the message "Shape protection and/or layer properties prevent execution of this command." under Microsoft Office VISIO (Version 2000 – 2007, to present?), then you know what I mean:



Fortunately, the solution to the problem is easy: Just right-click on the offending shape to modify its protection:



After activating the dialog, simply clear the Text check-box:



… and you will be allowed to do some really strange, bizarre things …



- like adding a text description to your Use Case Scenarios!

But wait – if you are going to have more than a single scenario, then rather than doing the same operation over, and over, and over, and over again, rather than doing something rational (like re-using that tool bar symbol), be sure to cut-and-paste that first shape a few dozen times.

(Hey: Wouldn’t it be great if those who developed our tools, had to use them?)


Enjoy,

-Rn

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